In automotive thermal management, coolant temperature in a cooling system is closely controlled for improved engine efficiency and emission. The cooling system may include a radiator as a primary heat exchanger, and a thermostat for controlling coolant flow through the radiator. For example, at one thermostat position, the coolant flow may bypass the radiator so that waste heat may be utilized to warm-up the engine. At another thermostat position, the coolant flow may pass through the radiator for maximum heat rejection. Degradation of the cooling system, such as thermostat degradation, may deteriorate engine fuel consumption and emission.
Other attempts for monitoring cooling system include comparing an estimated engine coolant temperature with a measured engine coolant temperature. One example approach is shown by Davison et al. in U.S. Pat. No. 6,302,065 B1. Therein, engine coolant temperature is estimated via a coolant temperature model. Based on the position of a thermostat, a high coolant temperature model or a low coolant temperature model is used for estimating the engine coolant temperature. Degradation of coolant temperature sensor and the thermostat can then be determined if the difference between the estimated and the measured engine coolant temperatures is larger than a threshold.
However, the inventors herein have recognized potential issues with such methods. As one example, coolant temperature in the cooling system oscillates responsive to the thermostat's position. The oscillation in coolant temperature may cause system degradation. For example, oscillation of coolant temperature in the radiator may cause expanding and contracting of different sections of the radiator, and may lead to radiator failure, such as leaking. Aside from leaking of the coolant, radiator failure may cause engine overheat and severe damage to the vehicle system. Further, when introducing hot engine coolant to the cold bulk coolant in the radiator, stagnated flow pockets are formed due to viscosity differences between hot and cold coolants. Radiator failures due to thermal strain and fatigue are more likely to occur near the areas of high temperature variations caused by either flow stagnation or intermittent flow.
In one example, the issues described above may be addressed by a method comprising: adjusting coolant flow with a thermostat; based on thermostat position, estimating a coolant temperature at a location between an end of a radiator core and a junction of a radiator lower hose and a heater core output line; and indicating cooling system health based on the estimated coolant temperature. In this way, cooling system health may be evaluated before occurrence of system degradation, so that procedures may be taken to prevent future system failure.
As one example, a method may determine radiator failure and thermostat degradation based on an estimated coolant temperature at a radiator outlet. The radiator outlet is defined as an opening on the radiator housing from where a lower hose is coupled to. The coolant temperature may be estimated as a mathematical function of a coolant flow rate at the radiator outlet. The direction of the coolant flow at the radiator outlet depends on thermostat position. The thermostat may be at a first position to stop low temperature coolant from the thermostat to the radiator, and at a second position to allow high temperature coolant from the thermostat to the radiator. A coolant pump in fluid communication with the radiator outlet may pump coolant to an engine block. In the radiator bypass mode, when no coolant flows to the radiator inlet from the thermostat, operating the coolant pump may create a low pressure condition from the pump inlet extending to the radiator outlet. The low pressure condition may draw hot coolant from the heater core to the radiator outlet via a radiator bleed line. Consequently, coolant temperature at the radiator outlet may be affected by the reversed hot coolant flow drawn from the heater core. By incorporating the reversed coolant flow into a model, coolant temperature oscillation in the cooling system may be accurately simulated. The model may further be used to estimate other engine operating parameters such as engine temperature and radiator temperature for improved engine control. By evaluating the estimated oscillation of coolant temperature, radiator failure may be predicated in real-time without requirement of additional hardware. By comparing the estimated coolant temperature to a measured coolant temperature at the radiator outlet, thermostat degradation may also be determined.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.